1. Field of the Invention
The present invention relates to disk drives. More particularly, the present invention relates to a disk drive that is responsive to flex bias changes imparted by a flex circuit cable during an idle mode of the disk drive.
2. Description of the Prior Art and Related Information
Today, computers are used at work, at home, and everywhere in between. Computers advantageously enable communication, file sharing, the creation of electronic documents, the use of application specific software, and electronic commerce through Internet and other computer networks. Typically, each computer has a storage peripheral such as a disk drive (e.g. a hard disk drive).
A huge market exists for hard disk drives for mass-market computer devices such as desktop computers, and laptop computers, as well as for small form factor (SFF) disk drives for use in mobile computer devices (e.g. personal digital assistance (PDAs), cell-phones, digital cameras), etc.
Typically, the main assemblies of a hard disk drive are a head disk assembly (HDA) and a printed circuit board assembly (PCBA). The head disk assembly includes an enclosure including a base and a cover, at least one disk having at least one recording surface, a spindle motor for causing each disk to rotate, and an actuator arrangement. The PCBA generally includes circuitry for processing signals and controlling operations in the disk drive.
An actuator arrangement that is commonly used in hard disk drives is a rotary actuator arrangement included as part of a head stack assembly (HSA) that includes a collection of elements of the head disk assembly. The collection typically includes certain prefabricated subassemblies and certain components that are incorporated into the head disk assembly. For example, a prefabricated head stack assembly (HSA) may include a pivot bearing cartridge, a rotary actuator arrangement, and permanent magnets and an arrangement for supporting the magnets to produce a magnetic field for a voice coil motor (VCM).
The rotary actuator arrangement of the HSA may also include a coil forming another part of the voice coil motor, an actuator body having a bore through it, and a plurality of arms projecting parallel to each other and perpendicular to the access of the bore. The rotary actuator arrangement of the HSA may also include head gimbal assemblies (HGAs) that are supported by the arms. Each HGA includes a load beam and a head supported by the load beam. The head is positioned over a track on a recording surface of the disk to write or read data to or from the track, respectively. A flex circuit cable typically connects the processing circuitry of the PCBA to the rotary actuator of the HSA in order to deliver commands such as read and write commands, as well as idle mode and power-off commands.
Minimizing power consumption is always a critical design consideration for disk drives, and, especially, for small form factor (SFF) disk drives for use in mobile computing devices. Hence, to minimize power consumption and meet recovery time characteristics, disk drives often employ an idle mode that is entered into after a pre-determined time period when there are no commands received from the host device. Typically, in the idle mode, particular electronics of the disk drive, such as the pre-amplifier and read/write channel are powered down. In the idle mode, the head of the disk drive typically floats on the disk media at a pre-determined location by a constant VCM current being applied to the actuator to compensate for the bias force imparted by the flex circuit cable (hereinafter the flex bias).
Because there is always variation in flex bias from disk drive to disk drive, the VCM current to hold the head at a pre-determined location of the disk media is typically pre-calibrated for a disk drive.
Unfortunately, the flex bias associated with the flex circuit cable may change due to a number of factors, the most significant of which is temperature. This has become especially problematic with SFF disk drives for use in mobile devices that are exposed to a wide variety of different temperature changes due to their mobile nature.
For example, if the flex bias significantly increases in a negative direction (e.g. toward the outer diameter (OD) of the disk) then any margin toward the OD may be eaten up by the flex bias change and the head could be pushed toward the OD. Once the head reaches a certain point and passes the OD margin zone, the head may accelerate with increasing bias force along the OD direction and hit the loading ramp of the disk drive with excessive force. As a result, the head may be damaged and potential head-land-on-media failure may occur.
On the other hand, if the flex bias force increases in a positive direction (e.g. toward the inner diameter (ID) of the disk), the head may drift to the inner diameter (ID) and hit a crash-stop. This may cause problems in that the ID crash-stop presents a location where there is no servo-position information and therefore the disk drive may take a much longer time to recalibrate and re-enter active mode.
Thus, due to flex bias changes associated with the flex circuit cable, deleterious effects may result during disk drive idle mode such as the head hitting the OD loading ramp or the ID crash-stop.